The recovery of copper, nickel, lead and zinc from their ores produces over 12 million tons of slag per year. Since 1900, some slags have been used for rail ballast, but usually large slag heaps have accumulated adjacent to the smelters. In recent years, at various mines in Europe and Australia, some smelter slags, usually copper smelter slags, have been ground to about -325 mesh and combined with Portland cement for use in cemented mine backfill, however, the rate of generation of the various slags still exceeds their utilization. No one, so far as is known, has produced high grade concrete for general use in construction work which requires large quantities of ASTM grades of concrete.
During the 1980's, the pozzolanic (cementing properties) properties of Canadian smelter slags were studied to evaluate the feasibility of their use as a partial Portland cement replacement in concrete and mine backfill. It was concluded that these slags could be so used. However, the results were much inferior to those obtained with regular Portland cement, particularly with steel blast furnace slag cement mixtures which only provided approximately 70% of the strength obtained by use of Portland cement and Portland cement/steel mill blast furnace mixtures. Consequently, the work was discontinued, it having also been found that economics and transportation costs were not feasible.
It has now been found that large slag heaps are leaching unacceptably high amounts of heavy metal values, and mining companies are seeking acceptable solutions to this growing problem. Also, environmental authorities are requiring that plans be formulated for long term permanent solutions.
It is an object of this invention to provide a method of using base metal smelter slag to manufacture predictable grades of low, medium and high strength concrete for general construction purposes, including mine backfill that will be equal to or better than that obtained with Portland cement and Portland cement/blast furnace slag mixtures.
A further object of the invention is to provide a method that converts the smelter slag to a slag having similar properties to steel mill blast furnace slag, from which acceptable grades of slag cement can be produced, and which also produce a pig iron by-product.